[dm-devel] [PATCH v2 2/2] dm unstripe: Add documentation for unstripe target

[Keith Busch]

On Tue, Dec 12, 2017 at 01:35:13PM +0200, Nikolay Borisov wrote:
> On 11.12.2017 18:00, Scott Bauer wrote:
> > +    As an example:
> > +
> > +    Intel NVMe drives contain two cores on the physical device.
> > +    Each core of the drive has segregated access to its LBA range.
> > +    The current LBA model has a RAID 0 128k stripe across the two cores:
> > +
> > +       Core 0:                Core 1:
> > +      __________            __________
> > +      | LBA 511|            | LBA 768|
> > +      | LBA 0  |            | LBA 256|
> > +      ⎻⎻⎻⎻⎻⎻⎻⎻⎻⎻            ⎻⎻⎻⎻⎻⎻⎻⎻⎻⎻
> 
> If it's 128k stripe shouldn't it be LBAs 0/256 on core0 and LBAs 128/511
> on core1?

Ah, this device's makers call the "stripe" size what should be called
"chunk". This device has a 128k chunk per core with two cores, so the
full stripe is 256k. The above should have core 0 owning LBA 512 rather
than 511 (assuming 512b LBA format).